Control system



Nov. 26, 1946- A. w. SWINGLE EI'AL 2,411,763

CONTROL SYSTEM 0' 1 Filed Feb. 2,-- 1944 Lon 5pm 851,6 aw

I lnven'tohsz /z AP'LTTO W.' Swingie,

George H. ettibone, Joseph E. Dill,

Their Attorney Patented Nov. 26, 1946 CONTROL SYSTEM Artro W. Swingle,Schenectady, George H. Pettibone, Scotia, and Josep N. Y., assignors toGen h E. Dill, Schenectady, eral Electric Company, a

corporation of New York Application February 2, 1944, Serial No. 520,728

4 Claims.

This invention relates to control systems, more particularly to systemsfor controlling the operation of an electric motor, and it has for anobject the provision of a simple, reliable, improved, and inexpensivecontrol system of this character.

A more specific object of the invention is the provision of a controlcircuit arrangement which minimizes heat losses resulting fromcirculating currents.

In carrying the invention into efiect in one form thereof, a splitseries field motor is utilized, together with a directional resistorconnected across the terminals of the field winding and a speedcontrolling resistor connected between an intermediate tap of thedirectional resistor and one side of the source. These resistors arecontrolled by banks of spring contacts which in turn are selectivelyactuated by high and low speed Selsyns.

In illustrating the invention in one form thereof, it is shown asembodied in the drive portion of a follow-up control system.

For a better and more complete understanding of the invention, referenceshould now be had to the following specification and to the accompanyingdrawing of which the single figure is a simple, diagrammatical sketch,partly in perspective, of an embodiment of the invention.

Referring now to the drawing, an electric motor III is connected todrive an object H into positional agreement with a remote controllingobject (not shown).

The motor III is a split series field type motor;

i. e., its field winding is divided into two field coils Ilia and Ilb ofopposite polarity to eflect rotation of the motor in either directionwhen the excitation of one field coil predominates over that of theother. The lower brush Iiic of the motor is connected to one side I 2 ofan A.-C. supply source I2, H. The upper brush I M of the motor isconnected to the common point of the two field coils Ito and llib.

A resistor I4 and a capacitor I! are connected in parallel across theopposite terminals of the field coils Ilia and lb by means of conductorsl8 and II. This resistor is referred to as the directional controlresistor. A second resistor II is connected between the center tap Ha ofresistor I4 and the side I2 of the A.-C. supply source. This resistor isprovided with a plurality of taps Ito, I8b, lie, Ild, and I88 to providefor short cireuiting portions of the resistor, thereby to vary the speedof the motor I0. Consequently, resistor I 8 is referred to as the speedvarying resistor.

To provide for short circuiting the portions of the resistor which aredefined by the taps "a to lie, inclusive, a plurality of spring contactsare provided. These contacts are arranged in two groups or banks It and20. As shown, the group I9 comprises contacts Illa to I9), inclusive,and the group 20 comprises contacts 20a to 20), inclusive. Both groupsof contacts are mounted on a supporting member 2|, with the individualcontacts separated from each other. The member 2| is preferably made ofa suitable insulating material.

The innermost contacts I91: and 20a of the two groups are connected tothe opposite terminals Ilb and I40, respectively, of the speed varyingresistor I4, and the contacts lab and 2017 are connected together to theterminal I8a of the speed varying resistor l8 and thus to the center tapHa of the directional resistor. The taps lab, I80, I8d, and the terminalI88 of the speed varyin resistor it are connected to the contacts lsc,ISd, I9e, and I9], respectively, of the group I9, and also tocorresponding contacts Zilc, 20d, 20c, and 20! of the group 20.Capacitors 22 and 23 are connected across the taps I and ltd and betweenmidtap I8d and the terminal lie.

The actuation of the contacts to control the speed of the motor I 0 iscontrolled by a high speed or "fine Selsyn receiver 24 and by a lowspeed or "c0arse Selsyn receiver 2!. These Selsyn receivers 24 and 25are electrically connected to high and low speed Selsyn transmitters,respectively, (not shown). The high speed Selsyn receiver 24 comprises arotor member 24a and a stator member 241) which, in this application, ismounted in ball bearings and is free to rotate. It is connected throughspur gearing 28 and worm gearing 28a to the shaft of the drive motor III. The ratio of the gearing is such that the ratio between therevolutions of the stator 24b and the driven object I I is a suitablenumber such as 36:1; i. e., the stator 2417 will rotate 36 times foreach revolution of the driven object I I.

The low speed Selsyn receiver 25 has a rotor member 25a and a rotatablymounted stator member 26b. The rotatably mounted stator 24!: of the highspeed Selsyn receiver is connected with the rotatably mounted stator 25bof the low speed receiver by means of gearing 21 having a ratio suchthat the low speed stator 25?) rotates at a very low speed with respectto stator 24b; e. g., one revolution for each 36 revolutions of the highspeed stator 24b.

For directly actuating the contacts of'the banks It and 20, a member28:: located in the space between the two banks and mounted on a lever28 is provided. The lever 28 is mounted in a suitable bearing 29 forrotation about the bearing Y axis. Rotation of the lever 28 is effectedby means of a heart cam assembly comprising a heartshaped cam 30 whichis secured to the shaft of rotor 24a and a cam follower 2| mounted on ayoke 22 which is pivotally connected to lever 28.

To provide for transferring the control of the contacts from the highspeed Selsyn receiver to aria-tee in one direction or the other by meansof two electromagnets 3d and 35. The selective energization of theoperating coils 3M and 35a of these electromagnets is controlled bymeans of a heart cam assembly 36 which is operated by the low speedreceiver 25, together with a pair of'directional contacts 31 and 38.

The operation is as follows: At any instant cur rents flow from one sideof the source through the armature ID of the follow-up motor, fieldcoils Ida and lob in parallel, upper and lower halves of the directionalcontrol resistor i l in parallel to the center tap Ma, speed varyingresistor it to the opposite side of the source. Since the upper andlower halves of the directional control resistor it are equal, thecurrents circulating through these halves to the field winding coils Maand liib are also equal. Consequently, the torques produced by thesecurrents are opposite so that the net torque acting on the armature I iszero and the motor is at rest. When the motor is at rest, thecirculating currents are reduced to a very low value, owing to the highohmic resistance of the directional resistor, and thus the standbylosses of the motor are reduced to a minimum.

Rotation of the rotors of the transmitters causes the rotors-Eda and 25ato rotate to follow the rotors of the transmitters. If the rotation ofthe rotor 29a is in a clockwise direction, the cam follower ill willhave a component of movement toward the right, thereby to rotate thelever 28 in a clockwise direction about the axis of bearing 29. Theclockwise rotation of lever 28 moves the member 280. into engagementwith contact i9q. As the clockwise rotation of the rotor 23a continues;contact i9a is moved into engagement with contact lsb, thereby shortcircuiting the half of the directional control reill the rotor 26a willrotate the heart cam do in a counterclockwise direction, thereby to movethe member 26a downward. The downward movement of member 28a relievesthe pressure on the contacts of bank it, thereby successively insertingthe sections of the speed controlling resistor i t in the armaturecircuit and reducing the speed of motor it. The separation of contactsthe and lab interrupts the short circuit about the upper half of thedirectional resistor it. This results in reducing theexcitation of thesplit field coil Ida to equalize the excitation of both split fieldcoils ltd. and, iEb and restore the standby zero torque condition of themotor ill.

The rotors'25a and 25b rotate simultaneously with the rotor 26a andstator 2th and in the same directions, respectively. Owing to the 36:1reducthrough the split field coil iila than flows through coil Iflb, anda net torque is developed which causes the motor ill to rotate in adirection which drives the stator 24b in a counterclockwise direction.Owing to the full amount of resistor l8 in the armature circuit of themotor, the rotation is at a slow speed. The rotor 24b continues torotate in the clockwise direction and at a speed which is equal to thedifierence between the speed of the transmitter rotor and the speed ofthe stator 26b. A continued clockwise rotation of the rotor 24a actingon the heart cam assembly causes the member 28a to continue its upwardmovement to close the contacts I90, i901, lee, and lQf in succession.With the successive closing of these contacts, successive sections ofthe speed varying resistor l8 are short circuited, thereby increasin thevoltage applied across the armature and field coil Ilia. As a result,the speed of the motor Ill increases until the speed of thecounterclockwise rotation of the stator 25b is equal to the speed of therotor of the transmitter. When this condition is reached, the rotor Zeais at standstill with the result that the speed of the motor i0 is notfurther increased.

If, now, the speed of the transmitter is decreased, the speed of thestator 24b does not decrease at first because it cannot change until thespeed of motor ill changes. Consequently,

tion of gearing 27, the amount of rotation of the rotor 25a and thestator 25b is only one-thirty sixth th corresponding rotations "of therotor 24a and the stator 24b of the high speed Selsyn receiver. l a

If the rotation of rotor 25a in a clockwise direction exceeds apredetermined amount, e. g., two and one-half degrees, the heart cam 30will have rotated to the -degree position, at which position it isdesirable to transfer control to the low speed Selsyn 25. The rotationof the heart cam assembly 36 closes contacts 37, thereby to energizeoperatin coil Ma. The armature 33 is attracted toward core member 36,thereby rotating lever 28 in a clockwise direction to close all thecontacts of bank is which may not have been closed by rotation of rotorEda. The speed of motor i0 is rapidly accelerated to its maximum value.As a result, the driven object ii is driven in the desired direction atmaximum speed and the stators 26b and 251) are driven in a counter.clockwise direction. When the counterclockwise speed of the statorsexceeds the speeds of the rotors of the transmitters to which they arerespectively connected, the rotors 2 5a and 25a will rotate in acounterclockwise direction. When the rotor 25a returns to within two andone-half degrees of its initial position with respect to the rotor ofthe low speed transmitter, the heart cam assembly 36 will open thecontacts 37, thereby to deenergize the operating coil Sta. As a resultof the deenergization of coil Sta, the armature 33 is no longerattracted by the core member 34 and, consequently, the control of thecontacts I9a to WI, inclusive, is restored to the high speed Selsyn 26.

If the initial rotation of the rotor Eda is in a counterclockwisedirection, in response to a rotation of the rotor of the transmitter ina direction opposite to that described in the foregoing, the operationwill be the same as that described except that the rotation of the heartcam 30 and lever 28 will be in a counterclockwise direction and thecontacts 20a to 20f, inclusive, of the lower bank 20 will be actuated.The closing of contacts 2M and 28b short circuits the lower half of thedirectional resistor I ti, thereby efiecting rotation of the motor ii!in the reverse direction. contacts 201), 20c, 29d, we, and 20 shortcircuits successive portions of the speed varying resistor E8 toaccelerate the motor H3 in the manner described in the foregoing.

Although in accordance with the provisions of the patent statutes, thisinvention is described as embodied in concrete form and the principlethereof has been explained, together with the best mode in which it isnow contemplated apply- The subsequent successive closing of ing thatprinciple, it will be understood that the apparatus shown and describedis merely illustrative and that the invention is not limited thereto,since alterations and modifications will readily suggest themselves topersons skilled in the art without departing from the true spirit ofthis invention or from the scope of the annexed claims.

What we claim as new'and desire to secure by Letters Patent of theUnited States is:

1. A control system comprising in combination, a split series fieldmotor having one armature terminal connected to an intermediate tap ofthe series field winding and a connection from the opposite armatureterminal leading to one side of a supply source, a resistor connectedacross said series fielding winding, a second resistor connected-from anintermediate tap of said first resistor to the opposite side of saidsource and having a plurality of taps, a plurality of spaced apartcontacts arranged in two banks, a contact of one of said banks beingconnected to one terminal of said first resistor and a correspondingcontact of the other bank being connectedto the opposite terminal ofsaid first resistor and each of the taps of said second resistor beingconnected to a different one o1 the contacts of one bank and to acorrespondin contact of the second bank, and means for selectivelyengaging the contacts of one of said banks to close in successionthereby to short circuit a selected portion of said first resistor toeffect rotation of said motor in a, corresponding direction andsuccessively to short circuit portions of said second resistor to varythe speed of said motor. I

2. A control system comprising in combination, a split series fieldmotor having one armature terminal connected to an intermediate tap ofthe series field winding anda connection from,

the opposite armature terminal to one side of a supply source, a firstresistor connected across said series field winding, a second resistorconnected from the midpoint of said first resistor to the other side ofsaid source and having a plurality of taps, a supporting member, aplurality of contacts mounted on said supporting member in cooperativespaced apart relationship and in two groups separated from each other toprovide a centrally disposed space,-the end contacts of said groupsadjacent said centrally disposed spacebeing connected to oppositeterminals of said first resistor, and a member mounted within said spacefor movement in opposite directions to selectively actuate said groupsof contacts and to close the contacts of the selected group insuccession thereby to short circuit a selected half of said firstresistor to efiect rotation of said motor in a selected direction andsuccessively to short circuit'portions of said second resistor to varythe speed of said motor.

3. A control system comprising in combination, a split series fieldmotor having one armature terminal connected to an intermediate tap ofthe series field winding and a connection from the opposite armatureterminal to one side of a supply source, a resistor connected acrosssaid series field winding, a second resistor connected from anintermediate tap of said first resistor to the opposite side of saidsource and having a plurality of taps, a pair of banks of springcontacts separated from each other to provide a centrally posltelydisposed electromagnets disposed space, each of said banks comprising aplurality of spring contacts mounted in spaced apart relationship, acontact of one of said banks being connected to one terminal of saidfirst re=- sistor and a corresponding contact of the other bank beingconnected to the opposite terminal oi said first resistor and each ofthe taps of said sec- 0nd resistor bein connected to a different one oi.the contacts of one of said banks and a corresponding contact of thesecond bank, an actuating member mounted in said centrally disposedspace for movement in opposite direction, a relatively high speed Selsynreceiver for movin said member in a selected direction to initiate thesuccessive closing of the contacts of the selected bank thereby to shortcircuit a selected portion of said first resistor to effect rotation ofsaid motor in a selected direction and to increase its speed, arelatively low speed Selsyn receiver, speed reducing gearing connectingsaid Selsyns, and means responsive to a predetermined amount of rotationof said low speed Selsyn receiver for moving said actuating member to anextreme position to close all of said contacts 01' said selected bankthereby to effect rotation of said motor at maximum speed.

4. A control system comprising in combination, a split series fieldmotor having one armature terminal connected to an intermediate tap ofthe series field winding and a connection from the opposite armatureterminal to one side of a supply source, a resistor connected acrosssaid series field winding, a second resistor connected from anintermediate tap of said first resistor to the opposite side of saidsource and having a plurality of taps, a pair of banks of springcontacts separated from each other to provide a centrally disposedspace, each of said banks comprising a plurality of sprin contactsmounted in spaced apart relationship, a contact of one of said banksbeing connected to one terminal of said first resistor and acorresponding contact of the other bank being connected to the oppositeterminal of said first resistor and each of the taps of said secondresistor being connected to a difierent one of the contacts of one ofsaid banks and a corre-- sponding contact of the second bank, apivotally mounted lever provided with an actuating menuber in said,centrally disposed space and also provided with an armature member, apair of oparranged in cooperative relationship with said armature foreifecting pivotal movement of said lever in opposite directions, arelatively high speed Selsyn receiver for moving said lever in aselected direction to initiate successive closing of the contacts of oneof said banks thereby to short circuit a portion of said first resistorto effect rotation of said motor in a selected direction, a relativelylow speed Selsyn receiver, speed reducing gearing connecting said Selsynreceivers, and means responsive to a predetermined amount of rotation ofsaid low speed Selsyn receiver for selectively energizing saidelectromagnets to move said lever to an extreme position to close all ofsaid contacts of said selected bank to efiect rotation of said motor atmaximum speed.

ARTRO W. SWINGLE. GEORGE H. PETTIBQNE. JOSEPH E. DILL.

